The present invention relates to a quantum-well electronic bolometer and its application to a detector of electromagnetic waves, in particular to a quantum-well semiconductor wave detector. This bolometer operates in the same manner as a hot-electron bolometer which allows, in contrast with known devices using quantum wells, to detect waves at normal incidence angles.
For example, the article of B. F. Levine et al published in Applied Physics Letters No 53, page 296, (1988), describes a quantum-well photoconductor including, as shown in FIG. 1, a stack of quantum wells each comprised of a layer of gallium arsenide (GaAs) (such as layer 1) flanked by two layers of aluminum-doped gallium arsenide (AlGaAs) (such as the layers 2 and 3). Electrodes 4 and 5 are provided at the upper part and at the lower part of the stack of layers. In such a device, the electrons are stored at their quantum energy level in the GaAs quantum well. Under an illumination, these electrons are excited into the conduction band of the potential barrier (AlGaAs) and are collected in the ohmic contacts (electrodes 4 and 5) located on either side of the quantum-well stack.
This type of detector has two disadvantages:
1. In the photoconductive mode, current is independent of the number of wells with constant electric field. A single well can detect the light, the structure biasing itself again to keep this current in the detector. This comes from the fact that, in this detector, the flux of photons is parallel to the flux of electrons.
2. As the motion of the electrons is quantized only in the direction of growth, only the internal electromagnetic field component normal to the quantum wells is detected. Thus, this device does not detect the incident waves normal to the surface, which makes their integration in two-dimensional systems very difficult, as described in the published documents:
K. W Goosen and S. A. Lyon, Applied Physics Letters, 53, 1027 (1988); PA0 G. Hasnam, B. F. Levine, C. G. Bethea, R. A. Logan, J. Walker and R. J. Molik, Applied Physics Letters, 54, 2515 (1989).
The first disadvantage has found a solution in the patent application No. 90 06932 filed on Jun. 5, 1990 (E. Rosencher and B. Vinter) by adopting a geometry with transverse ohmic contacts. The device described in that patent application includes at least a first quantum well and a second, non-doped, quantum well, a transfer of electrons from the first well to the second well being possible under the action of an incident radiation propagating slantwise with respect to the plane of the quantum wells. The detector includes in addition ohmic contacts located laterally relative to the two quantum wells.
The second disadvantage is eliminated by the present invention. The basic idea of the present invention is to use a physical phenomenon which is not sensitive to the polarization of light: the hot-electron bolometry.